Pyrogen squib



Oct. 12, 1965 K. R. FOOTE 3,211,097

PYROGEN SQUIB Filed June 29. 1964 INVENTOR. KENNETH R. FOOTE ATTORNEY.

United States Patent 3,211,097 PYROGEN SQUIB Kenneth R. Foote, China Lake, Califi, assignor to the United States of America as represented by the Secretary of the Navy Filed June 29, 1964, Ser. No. 379,053 6 Claims. (Cl, 102-28) (Granted under Title 35, US. Code (1952), sec. 266) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a pyrogen squib and more particularly to an igniter squib for the reliable ignition of pyrotechnic and propellant compositions.

At the present time many mechanical devices are designed to be operated by gas under pressure and it is not uncommon to provide a gas generating system as a portion of such devices. The conventional squib output consists generally of a short duration flash of hot gases and burning particles. Their use for ignition of pyrotechnic and propellant items, such as flares, smoke generators, gas generators, ignition grains, rocket motors, etc., normally requires the use of additional ignition materials to supplement the conventional squibs output. Pyrotechnic items using conventional squibs and supplementary ignition materials often prove to be diflicult to operate, bulky and expensive. This is especially the problem under adverse environmental conditions such as high altitude, high wind velocity, or low temperature.

The pyrogen squib of the present invention overcomes the aforementioned problems by providing a self-contained ignition assembly combined with a grain and nozzle plate inside a hermetically sealed case or body, which combination is capable of igniting most pyrotechnic and propellant formulations without aid from additional ignition materials.

It is therefore an object of this invention to provide a novel ignition squib which provides a directionally controlled flame jet for ignition of hard-to-ignite materials.

Another object is the provision of an ignition squib with a persistent flame jet of from 0.5-1.5 seconds duration.

A further object is to provide an ignition squib which is reliable at high altitudes.

Yet another object of this invention is to provide an igniter squib which will find use in underwater devices.

Still another object is to provide an igniter which is simple to package and relatively safe to handle.

A further object is to provide a squib device which can operate under confinement and maintain adequate gas pressure while the output material is being consumed.

A still further object of this invention is to provide a self-contained ignition device which will operate at low temperature.

Other objects and novel features of this invention will become apparent from the following detailed description of the invention when considered in connection with the accompanying drawing wherein:

FIG. 1 is a vertical sectional View of the pyrogen squib, subject of this invention;

FIG. 2 is a vertical section of the preassembled igniter assembly which constitutes the upper internal portion of the squib shown in FIG. 1;

FIG. 3 is a vertical section of the squib casing containing only the grain and nozzle plate of the squib shown in FIG. 1; and

FIG. 4 is an exploded view of the components of this invention.

Referring now to the drawings, there is illustrated in FIG. 1 the pyrogen squib of the present invention desig- 3,211,097 Patented Oct. 12, 1965 nated generally by numeral 10 and which comprises a cup shaped casing 12 having a weakened or thinned bottom portion 14, a nozzle plate 16 positioned within casing 12 adjacent portion 14 and having a single port 17; a booster grain 18 formed with an internal perforation 19, and an ignition assembly designated generally by numeral 20. Booster grain 18 consists of a flare composition and is positioned within casing 12 in abutting relation to nozzle plate 16, the diameter of the grain being just slightly smaller than the casing so that it will fit snugly against the casing wall. The edges of casing 12 are crimped into the ignition assembly for the purpose of hermetically sealing the squib.

FIG. 2 illustrates the ignition assembly 20 which is preassembled and comprises a plug member 22 made of thermosetting plastic and having an outwardly extending shoulder portion 24 of a diameter adapted to fit snugly within casing 12. Supported in member 22 are two lead wires 26 having ends terminating at the inner end of the member and connected by a coated bridgewire 28. The lead wires are adapted for connection to a suitable electrical source. Coated bridgewire 28 consists of a fine wire with a quick-fire initiation composition, to be described later, positioned around it. A spacer 32 in the form of an annulus or hollow cylinder have a bore 34 receiving the inner end of member 22, has one end thereof secured by appropriate means, such as cement, to shoulder portion 24 and the other end extending therebeyond into casing 12. Spacer 32 is made of a relatively easy-to-ignite material. The remainder of bore 34 is filled with an ignition composition 36, hereinafter described. A thin closure disc 38 made of suitable pyrotechnic material is positioned against the end of spacer 32 so as to enclose and seal the bore.

Referring now to FIG. 3 there is shown the squib casing 12 with nozzle plate 16 and booster grain 18 positioned therein. Casing 12 may be made of any suitable material. Guilding metal is used in the present embodiment. The closed bottom portion 14 is weakened by impacting, drawing or coining until its thickness is approximately .0030"i.0015 as compared to .008":.001, the average thickness of the remainder of the casing. The thinned section must not be porous or cracked. The preferred form of weakening is by drawing or impacting because no sharp changes in the thickness of the metal are produced as is the case when the weakening is accomplished by coining. Nozzle plate 16 may be of any suitable material. The plate used herein is a stainless steel single orifice plate about .032i.002" thick, about .250 in diameter with an orifice or port 17 of about .055"-' .002".

The flare composition of which the booster grain 18 is made, and which has contributed to the success of this igniter at simulated altitudes of 192,000 feet, consists essentially of 54:2% by weight magnesium, 30i2% by weight Teflon and 16- -2% by weight Viton. Teflon is the tradename for polytetrafluoroethylene and Viton is the tradename for a rubbery copolymer of vinylidene fluoride and perfluoropropylene. The composition is mixed in accordance with standard procedures, cured and then compressed at 7500 to 10,000 p.s.i. Internal perforated booster grain 18 is manufactured with an outside diameter of about .250":.002" (slightly less than casing or cup 12 so that it will slide snugly into said casing). The internal perforation 19 is about .100i.002" in diameter and is positioned in alignment with the single port 17 of nozzle plate 16.

The materials used in this squib were mainly responsible for its success under the adverse environmental conditions for which it was developed. In FIG. 5 there is shown an exploded view of the components. Plug member 22 may be of any suitable insulating pressure seal material; the thermosetting plastic, phenolic resin, is preferred. Lead wires 26 composed of copper wire are molded into th resin. No spine cavity should be permitted to extend to the base lead wire and the insulated wire should not be permitted to move away from the plug. For this invention each lead wire withstood a pull test of pounds without visibly loosening the plug. Bridgewire 28 is connected to the ends of lead wires 26 by welding, soldering or other suitable means and is made of platinum-iridium alloy with a resistance between 180 and 225 ohms per foot at C., and a breaking strength of not less than 60 grams. The resistance of the bridgewire circuit measured between the lead wires should be not less than 0.7 ohm nor more than 1.3 ohms. It should be obvious that either the same resistance could be formed of other conductor materials or that the amount of resistance could be varied depending upon the nature of the electric circuit and the degree of sensitivity desired. Bridgewire 28 is coated with an extremely easily ignitable substance 30 generally termed a quick-fire initiation composition which is ignited by passing a current through the bridgewire. The initiation composition may be chosen from a wide variety of materials and such selection is well within the cognizance of those skilled in the art. Initiation composition or quick-fire substance 30 which proved most successful in the present invention consists essentially of 34.7% by weight lead styphnate, 19.3% by weight zirconium, 45.2% by weight lead peroxide and 0.8% by weight gum arabic binder. These materials are blended together and painted or beaded on bridgewire 28 The plug, leadwires and headed bridgewire are placed in an oven for about 16 hours at 115-140 F., then coated with ethyl cellulose lacquer. Spacer 32 is manufactured from the same type flare composition as booster grain 18 disclosed hereinbefore. Ignition composition 36 may be selected from a variety of igniter compositions. However, the composition found to be most successful under the conditions to which this squib was subjected consists essentially of a homogeneous mixture of 97% by weight lead dioxide and 3% by weight amorphous boron. About 80 milligrams of this composition are loose-filled int-o bore 34 so as to cover coated bridgewire 28. After loading, closure or seal disc 38 is cemented to the bottom of the spacer with Viton cement or other suitable bonding material. Closure disc 38 is a thin wafer element about .250"- .002" in diameter and .005":.002" thick made from the same compressed flare composition as spacer 32 and grain 18. However, the exact nature of the disc is not critical, it being necessary only that it be of a thickness and a material which will be destroyed by burning of the igniter components of the ignition assembly.

To assemble: Load nozzle plate 16 and booster grain 18 into casing 12. Compress the preassembled ignition assembly 20 into casing 12 and crimp the edges of the casing securely over plug member 22. Care should be taken not to deform in any way the bottom portion 14 of casing 12 which is either thinned or coined. The crimp should be sufficiently strong to prevent the casing from separating from the plug member during functioning.

While the above detailed description of the structure and materials of the pyrogen squib which form the subject matter of this invention are considered to be adequate to make the operation thereof understandable, it is nevertheless considered expedient to give a short description of the operation of the present invention.

Upon the passage of an electrical current through lead wires 26 and coated bridgewire 28, the latter is heated and the initiator or quick-fire coating ignites. This ignites the ignition material 36 which substantially fills the space defined by the walls of the spacer and plug member. The flame and gases created by this burning rapidly destroys seal or closure disc 38 and ignites booster grain 18. The gas pressure created by this action is directed through nozzle port 17 rupturing the thinned bottom portion 14 of casing 12, in a matter of microseconds whereby a persistent flame jet of from 0.5 to 1.5 seconds duration is directed against the object to be ignited. The persistent directional flame jet produced by this invention is about four times the duration of conventional squibs.

From the foregoing, it should be evident that this invention provides an improved device in which ignition of the main gas producing material is reliably achieved more quickly than heretofore. This novel result is achieved by the provision of properly related igniter components of selected materials which provide a directionally controlled, persistent flame jet which operates under conditions where other igniters have failed.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the amended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A pyrogen squib comprising an igniter assembly;

a cup-shaped casing receiving said assembly and secured thereto, the end of said casing being spaced from said assembly to define a compartment, said end being weakened so as to be about one-third the thickness of the walls of said casing;

said compartment being substantially filled with an internal-perforated booster grain and single port nozzle plate;

said igniter assembly comprising a plug member;

a pair of lead wires extending through said member, having their outer ends adapted for connection to an electrical source;

a bridgewire connecting the inner ends of said wires;

an initiation composition positioned around said bridgewire;

said composition consisting essentially of 34.7% by weight lead styphnate, 19.3% by weight zirconium, 45.2% by weight lead peroxide and 0.8% by weight gum arabic binder;

a hollow spacer mounted to said plug member, the interior of said spacer defining a bore in which are located said bridgewire and said composition;

an ignition composition substantially filling the remainder of said bore; and

a closure disc mounted firmly against said spacer so as to seal said bore.

2. The squib as defined in claim 1 in which the spacer, closure disc and booster grain each consist essentially of 54% by weight magnesium, 30% by weight polytetrafluoroethylene and 16% by weight copolymer of vinylidene fluoride and perfluoropropylene.

3. The squib as defined in claim 2 in which the ignition composition consists essentially of 97% by weight lead dioxide and 3% by weight amorphous boron.

4. A pyrogen squib comprising a cup-shaped metal case having a weakened bottom portion;

a thermosetting plastic plug member having an outwardly extending shoulder portion adapted to seal the open end of said case and fill a portion thereof;

a pair of lead wires extending through said plug member;

a bridgewire having a resistance ranging from 0.7 to 1.3 ohms connecting said wires internally of said member;

an initiation composition positioned around said bridgewire; said composition consisting essentially of 34.7% by weight lead styphnate, 19.3% by weight zirconium, 45.2% by weight lead peroxide and 0.8% by weight gum arabic binder;

a spacer in the form of an annulus having one end secured by appropriate means to the shoulder of said plug member, the interior of said spacer defining a bore in which are located said bridgewire and initiation composition;

an ignition composition substantially filling the remainder of said bore;

a closure disc secured against the other end of said spacer so as to retain said ignition composition within said bore;

a single-port nozzle plate positioned within said case and adjacent said weakened portion; and

an internal perforated booster grain filling the remainder of said case, one end abutting said closure disc and the other abutting said nozzle plate.

5. The squib as defined in claim 4 in which the spacer, disc, and grain each consists essentially of 54% by weight magnesium, 30% by weight polytetrafluoroethylene and 16% by weight copolymer of vinylidene fluoride and perfluoropropylene.

6. The squib of claim 5 in which the ignition composition consists essentially of 97% by weight lead dioxide and 3% by weight amorphous boron.

References (Iited by the Examiner UNITED STATES PATENTS 2,079,777 5/ 37 Taylor et a1. 102-28 2,801,585 8/57 Smith 102-28 3,135,200 6/64 Jackson 102-28 References Cited by the Applicant UNITED STATES PATENTS 20 BENJAMIN A. BORCHELT, Primary Examiner. 

1. A PYROGEN SQUIB COMPRISING AN IGNITER ASSEMBLY; A CUP-SHAPED CASING RECEIVING SAID ASSEMBLY AND SECURED THERETO, THE END OF SAID CASING BEING SPACED FROM SAID ASSEMBLY TO DEFINE A COMPARTMENT, SAID END BEING WEAKENED SO AS TO BE ABOUT ONE-THIRD THE THICKNESS OF THE WALLS OF SAID CASING; SAID COMPARTMENT BEING SUBSTANTIALLY FILLED WITH AN INTERNAL-PERFORATED BOOSTER GRAIN AND SINGLE PORT NOZZLE PLATE; SAID IGNITER ASSEMBLY COMPRISING A PLUG MEMBER; A PAIR OF LEAD WIRES EXTENDING THROUGH SAID MEMBER, HAVING THEIR OUTER ENDS ADAPTED FOR CONNECTION TO AN ELECTRICAL SOURCE; A BRIDGEWIRE CONNECTING THE INNER ENDS OF SAID WIRES; AN INITIATION COMPOSITION POSITIONED AROUND SAID BRIDGEWIRE; SAID COMPOSITION KCONSISTING ESSENTIALLY OF 34.7% BY WEIGHT LEAD STYPHANATE, 19.3% BY WEIGHT ZIRCONIUM, 45.2% BY WEIGHT LEAD PEROXIDE AND 0.8% BY WEIGHT GUM ARABIC BINDER; A HOLLOW SPACER MOUNTED TO SAID PLUG MEMBER, THE INTERIOR OF SAID SPACER DEFINING A BORE IN WHICH ARE LOCATED SAID BRIDGEWIRE AND SAID COMPOSITION; AN IGNITION COMPOSITION KSUBSTANTIALLY FILLING THE REMAINDER OF SAID BORE; AND A CLOSURE DISC MOUNTED FIRMLY AGAINST SAID SPACER SO AS TO SEAL SAID BORE. 